The present invention relates to image forming equipment such as an electrophotographic or electrostatic copier, facsimile transceiver or printer and, more particularly, to image forming equipment of the type having a cleaning device which removes a developer from a photoconductive element after image transfer and collects it in a collecting section thereof.
Image forming equipment of the type described develops a latent image electrostatically formed on an image carrier by a developing device, transfers the developed image to a recording medium, and then removes the developer remaining on the image carrier by a cleaning device and collects it in a collecting section of the cleaning device. The equipment determines whether or not the developer collected in the collecting section has reached a predetermined amount by determining whether or not a fresh developer has been supplemented to the developing device a predetermined number of times. This stems from the fact that when the equipment repeats an image forming cycle with a single supplement of developer, the amount of developer to be collected in the collecting section is substantially fixed by the type of the equipment and, therefore, the developer collected in the collecting section reaches a predetermined amount when a developer is supplemented a particular number of times.
Japanese Patent Publication No. 40990/1989, for example, discloses equipment having a concentration sensor responsive to the decrease in toner concentration beyond a predetermined one. On such a decrease in toner concentration, a toner supply device for feeding a toner to a developing device is driven. If the toner concentration does not increase to the predetermined concentration within a predetermined period of time despite the feed of toner, the equipment turns on an alarm lamp to urge the operator to supplement a toner to a hopper thereof by determining that the hopper has run out of toner. At the same time, the equipment adds "1" to a memory which counts the number of times that a toner is supplemented. Thereafter, the memory is incremented by "1" every time a toner is supplemented to the hopper, i.e., every time the alarm lamp is turned on. When a toner is supplemented a predetermined number of times, meaning that a predetermined amount of toner is collected in a filter bag constituting the collecting section, a lamp for informing the operator of the time for inspecting the equipment is turned on.
The conventional scheme described above has a drawback left unsolved, as follows. The memory for counting the number of times of toner supply is incremented by "1" at the instant when the alarm lamp for urging the operator to supplement a toner to the hopper is turned on due to the toner concentration having failed to increase within a predetermined period of time, as stated above. It follows that even when a toner is actually not supplemented, it is determined that a toner has been supplied once. The conventional equipment, therefore, cannot count the number of times of toner supply with accuracy.